Uplink control information may consist of scheduling request, acknowledgement/non-acknowledgement (ACK/NACK) for a downlink (DL) transmission, a downlink channel state information and the like. In this case, ACK/NACK information on the DL transmission is control information fed back to a DL transmission entity by a DL reception entity in accordance with whether decoding of DL data is successful. In particular, if the DL reception entity successfully completes the decoding of the DL data, it may feed back the ACK information to the DL transmission entity. Otherwise, the DL reception entity may feed back the NACK information to the DL transmission entity.
Meanwhile, in order to support a bandwidth extended more than that of a related art, introduction of multiple carrier technology is taken into consideration. The multiple carrier technology may be called carrier aggregation technology. This carrier aggregation is the technology of brining an effect of using a logically wide frequency bandwidth by binding multiple carriers together in a frequency domain, whereas a single carrier is used by a general wireless communication system of a related art. If the multiple carrier technology is applied to a DL transmission, a plurality of DL data can be transmitted via a plurality of data channels on a plurality of DL carriers (or DL cells) at a specific time. Hence, a DL reception entity may be requested to feed back a plurality of ACK/NACK informations on a plurality of the DL data to a DL transmission entity.
Moreover, in TDD (time division duplex) system having a DL transceiving and a UL transceiving performed in different times (e.g., subframes), a plurality of ACK/NACK informations on a plurality of DL data transmitted in a plurality of DL subframes may be requested to be fed back.
Meanwhile, in order for a base station to measure a quality of an uplink (UL) channel from a user equipment, a signal (e.g., a reference signal (RS)) known to both of the base station and the user equipment may be available. For instance, a sounding reference signal (SRS) is periodically transmitted to a base station by a user equipment. Having receives the sounding reference signals from user equipments, the base station measures a UL channel, allocates a UL resource to each of the user equipments, and may then able to inform the corresponding user equipment of the result of the UL resource allocation.